1. Field of the Invention
The present invention relates to the structure of a snorkel duct preferably for use in an all terrain vehicle, such as a four-wheel buggy vehicle.
2. Background Art
A snorkel duct in all terrain type vehicles needs to open at a position at which water, mud, snow, dust or the like is unlikely to invade the air intake system of the vehicle. Accordingly, it would appear obvious to increase the length of air intake pipe to a distance that would prevent ingestion of solid or liquid contaminates. However, air flow resistance is consequently increased as the length of the intake pipe is increased. An example of a vehicle having such a long snorkel duct is disclosed in Japanese Patent No. 2873938.
In the conventional intake system of described above, a plate-like flange is formed at a position deviating from an intermediate portion of the intake duct in order to effectively reduce the intake passage by as much as forty to seventy percent. This arrangement is utilized in order to maintain a proper air-fuel ratio independently of engine speed.
However, increasing the cross sectional area of the intake opening in this arrangement by widening the snorkel duct in order to reduce the air-flow resistance is liable to deteriorated any silencing effects of intake noise. This type of arrangement will also limit the potential layout of the intake system of any vehicle for which it is employed, thereby reducing frame design and the positioning of components. Further, when the length of the intake pipe is substantially increased as in the conventional art, undesirable noises are caused by pulsations of air flow through the snorkel duct and intake pipe.